1. Field of the Invention
The present invention relates generally to the field of building construction using precast concrete components. More specifically, the present invention discloses a building system using modular precast concrete components that generally eliminates the use of large shear walls or moment frames to resist lateral loads.
2. Statement of the Problem
Most precast building structures, specifically parking structures, use large shear wall 140 or light wall 150 elements as the primary mechanism for resisting lateral loads, as shown for example in FIG. 1. Columns 110 are generally used to resist gravity loads. Though shear walls 140 and light walls 150 in conventional precast structures also can support gravity loads, the lateral and gravity load resistances are generally mutually exclusive in the overall behavior of the structure.
Examples of conventional precast framing are shown in FIGS. 1-5. One conventional approach uses precast double tee beams 120 spanning up to about sixty feet between light walls 150 or inverted tee beams 130 to create the floor system. The double tee beams 120 and inverted tee beams 130 generally bear on corbels 170 that project off the faces of the columns 110, pilasters 180 or spandrels 160. The inverted tee beams 130 are generally supported by columns 110 or shear walls that have pilasters 180 (i.e., an integral column). Due to the inherent separation of the components for resisting lateral loads and gravity loads in such construction systems, and because the columns are not lateral load resisting elements, conventional precast structures lose the economic advantages of combining both.
As a result, such precast structures tend to lack some of the other benefits seen in cast-in-place construction. Cast-in-place structures are perceived to be more open and provide better lighting distribution than precast structures. There is also a perception that cast-in-place structures are more resistant to cracking because the floor deck is post-tensioned and has fewer joints. Additionally, because cast-in-place structures inherently provide continuity in the floor deck, they are stiffer than precast floor decks. Due to the fact that precast structures generally use shear walls and light walls as the lateral resisting elements, the structures tend to feel closed off. Cast-in-place construction generally makes use of moment-frame systems to resist lateral loads, which allow for increased openness and lighting distribution. Therefore, a need exists for a precast building solution that provides greater openness, better light distribution, a stiffer floor deck and that largely eliminates the need for large shear walls and light walls to thereby enhance visibility within the structure.
3. Solution to the Problem
The present invention addresses these shortcomings of prior-art precast building systems by using bulb tee beams, shallow corrugated slabs and double tee beams supported on small walls that also function as columns and are distributed within the building footprint to open up the structure. In particular, as shown in FIGS. 6-13, the top flange of the bulb tee beams 230 supports the corrugated slabs 220 and double tee beams 120. The bulb tee beams 230 generally bear on corbels 170 and span in the same direction as double tee beams 120 in traditional precast construction. However, they have a much larger spacing which creates more openness.
Corrugated slabs 220 span between the bulb tee beams 230 and the sections can be both designed for maximum performance and efficiency. These slabs 220 are extremely shallow when compared to what has been used in traditional precast structures. The corrugated slabs 220 can also be connected to adjacent members by a keyway 240 as seen in FIG. 8(a). This keyway 240 allows for additional stiffness and strength at the joint to effectively seal the joint from moisture penetration. Preferably, the corrugated slabs 220 are also reinforced with negative moment rebar as seen in FIG. 10(a) at the ends to promote continuity that also increases the strength and stiffness of the floor deck.
The walls 210 act as vertical cantilevers to support the structure laterally as well as vertically. The walls 210 are oriented in such a manner that they take the lateral force in the long direction of the wall, and are turned ninety degrees where needed to take the same force in the other direction. The wall spacing and orientation allows for a dramatically open space.
At the ends of the structure, double tee beams 120 can be used for the longer floor spans and are supported by spandrels 160 on one end and bulb tee beams 230 on the other. This eliminates drop beams typically seen both in precast and cast-in-place structures for greater openness and light distribution.